Recovery behavior of amorphous poly(ethylene terephthalate) film uniaxially drawn at different temperatures

Homogeneously deformed amorphous poly(ethylene terephthalate) (PET) film sa mples were obtained by uniaxial drawing at temperatures from near the glass transition temperature T-g to far above T-g. Isothermal dimensional recove ry behavior was studied for the free stress state of the deformed sample. I t was shown that the dimensional recovery behavior of samples drawn near T- g was different from that of a sample drawn about 20 degrees C above T-g, i ndicating that the deformation mechanisms changed when the drawing temperat ure rose from near T-g to far above T-g. Recovery curves of samples drawn n ear T-g show two distinct steps in log time scale; the second step follows a single exponential function. The infrared measurement of a drawn sample s howed that the dichroic function decreased during recovery in the first ste p and was almost invariant at a very low value (<0.03) in the second step. However, the recovery curve of samples drawn about 20 degrees C above T-g d emonstrated nearly a straight Line in log time scale.